1. Field of the Invention
This invention relates generally to encryption technology and especially to encryption of video and/or audio broadcast signals.
In particular, the subscription broadcast system of this invention concerns an encryption protocol with steganographic supplementation.
2. Background Information
Service distribution organizations, such as cable and satellite providers, broadcast television and/or radio programs intended for reception by only those subscribers who have paid for the respective service. Conditional access to pay-TV broadcast signals is generally maintained by encryption and/or scrambling techniques. Subscribers who purchase these services usually receive a set-top terminal or “box” from the service provider. The set-top terminal is essentially a microprocessor that contains an integrated circuit chip programmed for decoding the incoming encrypted audio/video signals.
A problem with this security arrangement is that the set-top terminal is subject to theft and can then distributed to unauthorized users. Another shortcoming is that the encrypted signals entering the set-top terminal can be analyzed for determining the encryption algorithm. The decoding “chip” can then be duplicated so as to bypass the service provider set-top terminal for illegally accessing the broadcast signals.
Another technique for restricting access to encrypted signals is through an addressable set-top terminal and by assigning a unique personal identification code to the subscriber. The identification code provides authentication of the subscriber, and is transmitted from the set-top terminal to the service provider. If the identification code confirms that the subscriber is entitled to receive the program, the set-top terminal receives an approval signal from the service provider for programming the terminal to decrypt the signal. A deficiency of this security mechanism is that by bombarding the decoder “chip”, in a brute force attack with many different signals, it is possible to discover the approval signal. In a modified format, the identification code is continually being changed e.g. by a clock signal, however this system can be defeated by disabling the timing signal generator.
Some cable and satellite providers use electronic “smart cards” to control subscriber access. The “smart cards” typically plug into a card reader slot located in the set-top terminal. The “smart cards” contain an integrated circuit chip that holds the “key” that unlocks the encryption algorithm. U.S. Pat. Nos. 5,878,134, and 5,426,701 describe some of these devices. A limitation of decryption cards is that they are readily “broken” by pirates and duplicated or often stolen for unauthorized decryption.
Encryption/decryption techniques have been developed that utilize a combination of encrypted signals, such as shown in U.S. Pat. Nos. 5,243,650 and 4,636,851. A deficiency of many of these systems is that the decryption code is continually being transmitted thus subjecting the code to be more readily detected, intercepted and deciphered.